Ventricular fibrillation is currently a major cause of sudden death. The continuing objective of our research effort is to contribute to the development of a standby automatic implanted defibrillator system which will be suitable for use in patients who are at high risk of having out-of-hospital episodes of ventricular fibrillation. In the immediate future we plan to: (a) design and fabricate a prototype system(s) suitable for long-term evaluation in animals, (b) initiate chronic studies for evaluating the effectiveness of epicardial electrode systems for achieving ventricular defibrillation in dogs, (c) conduct additional acute studies involving epicardial electrodes in calves and (d) undertake relatively short-term chronic studies concerning chest wall electrode systems in calves.